Method and apparatus for distributing particulate over a given substrate are generally known in the art.
Typical applications for such method and apparatus are found in the field of agriculture where particulate spreaders are utilized to deposit seed and fertilizer.
Other prior art applications include the distribution of particulate in the form of gravel and/or de-icing compounds onto the surfaces of roadways during periods of inclement weather. Still other applications include the delivery of a powder coating reactant to the surface of a glass sheet while the glass sheet is maintained in an oxidizing atmosphere at a temperature sufficient to pyrolize the coating reactant to deposit a metal oxide film on the surface of the glass. One such method is disclosed in U.S. Pat. No. 4,344,986 issued to Henery on Aug. 17, 1982. In the disclosed embodiment, Henery employs a screw feeder for the reactant powder and an eductor to entrain the powder into a gaseous stream. A series of baffles project into the entrance of the coating chamber to create turbulence in the power/gas mixture, therebly allegedly improving the uniformity of coating. The discharge of the slotted nozzle is oriented substantially perpendicular to the surface of the glass sheet, which preferably moves beneath the nozzle to provide a complete coating by the discharged powder.
Recent advances in the field of absorbent structures such as disposable diapers have, however, given rise to a need for method and apparatus to substantially uniformly distribute discrete particles within a predetermined portion of the absorbent cores utilized in such structures so that the particles occupy less than 100% of the area in which they are distributed.
Although prior art absorbent structures useful as absorbent cores in products such as disposable diapers, incontinent pads, catamenial products, and the like have generally been comprised primarily of absorbent fibrous materials such as absorbent papers, absorbent cloths, fibrous batts, and the like, a relatively new class of compounds commonly known as superabsorbent polymers have been developed and are gaining increasing use as at least a part of such absorbent structures. Such superabsorbent polymers are normally water insoluble polymeric materials capable of absorbing at least 15 times their weight of water. Such superabsorbent polymers are available in a variety of forms, including flakes, powders and granules. Superabsorbent polymers generally differ from many conventional absorbent materials in that once an aqueous fluid is absorbed by most superabsorbent polymers, it generally cannot be expressed from the superabsorbent polymer under moderate pressure. This is often highly desirable in an absorbent structure such as a disposable diaper in that it prevents absorbed fluid from being expressed out of the structure.
When most superabsorbent polymers absorb aqueous fluids, they swell substantially, often to double their dry dimensions or more at saturation. At most superabsorbent polymers absorb fluid and swell, they generally become a gelatinous mass. If the superabsorbent polymer is in a particulate form and the particles are close to one another, they can coalesce and form a gel barrier which can block the flow of fluid.
Thus, for maximum effectiveness of the superabsorbent polymers, absorbent structures which include such materials in particulate form preferably maintain separation of the particles from one another to permit maximum absorption and swelling without allowing the particles to coalesce and form a gel barrier.
Prior art particle distribution techniques such as those described earlier herein have not been successful in providing substantially uniform distribution of the particulate superabsorbent polymer when employed on converting lines which are typically utilized to construct absorbent fibrous core structures at speeds of over 500 feet per minute.